1. J. Albert, Algebraic properties of bag data types, Proc. 17th Internat. Conf. on Very Large Data Bases, Barcelona, 1991, pp. 211–219.
2. N. Blanchard, Théories cardinales et ordinales des ensembles flous, Ph.D. Thesis, University of Lyon I, 1981.
3. The development of multiset theory;Blizard;Modern logic,1991
4. P. Bosc, F. Connan, D. Rocacher, Flexible querying in multimedia databases with an Object Query Language, Proc. 7th Internat. Conf. on Fuzzy Systems (FUZZ IEEE’98), Anchorage, 1998, pp. 1308–1313.
5. SQLf;Bosc;IEEE Trans. Fuzzy Systems,1995